In the manufacture of false twist textured yarn, the yarn strand is normally passed through a false twist spindlette which mechanically imparts a physical twist to the yarn. The twist imparted to the yarn backs up opposite to the direction of the yarn travel into a heated zone such as provided by a heated chamber or hot plate and the twist in the yarn is set to produce a torque in the yarn. When the strand of yarn emerges from the spindlette, substantially all of the imparted twist disappears opposite to the original twist inserted and the torque is retained in the yarn. This procedure is well known and disclosed in many patents, e.g. U.S. Pat. No. 2,777,276 and U.S. Pat. No. 3,267,657. Also, it is known to impart false twist to yarns, particularly thermoplastic synthetic yarns, by using a friction false twisting device. In these devices, the twist is imparted to the yarn by frictional contact between the yarn and a rotating surface. Examples of such false twisting devices are shown in U.S. Pat. Nos. 3,094,834; 3,227,461; 3,327,463; 3,816,993 and 3,872,661.
It has been found that in some instances, particularly with the use of a spindlette, small spots of the imparted twist along the yarn do not cancel out and are referred to as "tight spots." These spots usually occur when the imparted twist has not been completely and uniformly removed during passage through the spindlette. Also, the tight spots may result from fusion of adjacent filaments in the original twisted configuration during the heat setting operation or from retention of the reverse twist imparted to the yarn emerging from the spindlette at a weak portion of the yarn. Thus, the tight spot may have either a "Z" or "S" twist configuration. The tight spots are particularly objectionable because they cause distortion in the surface characteristics of a fabric produced from the yarn. Heretofore, devices such as off-set pins have been used below the spindlette to assist in the removal of the originally imparted twist by drawing the strand over the pins under pressure. Although the off-set pin method has helped to some degree, it is not completely satisfactory since several tight spots remain and the tension of the yarn on the pins tends to give poor fiber quality. Also, U.S. Pat. No. 3,338,830 discloses the use of a textile lubricating composition to reduce the number of tight spots in a false twisted yarn.
In accordance with the present invention means are provided for more uniformly cancelling the original twist from the yarn strand as the yarn emerges from the spindlette without adversely reducing the torque. More particularly, the method and apparatus of the present invention uses a tapered flange, yarn-driven, roller which serves to remove or reduce the tight spots occurring in the yarn.
It has been known to use a roller having a tapered flange or conical portion in order to create torque in a running length of continuous multi-filament yarn. In particular, U.S. Pat. No. 3,559,391 discloses an apparatus for the production of torque yarn wherein the twisting means comprises a freely rotatable or yarn-driven, roller having a cylindrical yarn driven end and a tapered or conical yarn twisting end for imparting twist to the yarn. In accordance with this patent synthetic thermoplastic yarn is passed in one or more helical wraps about the freely rotatable roller so that the yarn has a total angular contact of at least 360.degree. with the roller. As disclosed in this patent, a yarn of nylon, polyester or the like is fed from a yarn package by feed rollers over a stationary guide and from the guide the yarn is passed to a heating means such as a heated roller or the like which serves as a twist setting means. Then, the heated yarn is passed around the freely rotatable tapered roller and a driven roller or godet and subsequently passed to a wind-up package or a like device. As disclosed in column 6, beginning with line 40 of this patent, the freely rotatable, tapered roller is mounted substantially perpendicular to a supporting surface and is arranged with respect to the means feeding the yarn thereto so that the yarn will be urged across the tapered twisting portion of the roller designed to impart optimum helical twist characteristics to the yarn upstream between the roller and the twist setting means. In this arrangement, the tapered roller is used to impart all the twist required for the production of the torque yarn.
The patent to Gilchrist (U.S. Pat. No. 3,656,288) discloses a method and apparatus for texturing, i.e. crimping, a yarn wherein the yarn is subjected to a first false twisting operation in one direction in which the yarn is heated in the first twisting configuration and then the yarn is subjected to a second false twisting operation in the opposite direction without further heating. In this method the yarn is oppositely twisted by the second false twisting operation while the yarn still possesses sufficient heat to be at least permanently deformable. As described in this patent, the method of crimping includes heating the yarn, subjecting the yarn to a first false twisting operation in one direction and then immediately subjecting the yarn to a second false twisting operation in the opposite direction, with the twist imparted by the two false twisting operations usually being equal in magnitude so as to superimpose an opposite crimp onto the initially applied crimp in the yarn. Patentees particularly point out at the top of column 5, that crimped yarn is obtained which, compared to conventional single false twist crimped yarn, has greatly reduced or even zero torque, less stretch, but good bulkiness and has no tendency to snarl. In all the examples in this patent, the yarn was twisted to the same number of turns per inch in each false twisting operation, with the second false twisting operation applying the twist in opposite direction to the first. It is, therefore, apparent that a primary purpose of this patent is to provide a method for producing a substantially non-torque crimped yarn which will overcome the disadvantages of the yarn produced by conventional crimping techniques, that is, such yarns have high torque so that when knitted they tend to produce a fabric of high spirality.
There are other patents which also disclose processes and apparatus for imparting successive texturing operations to a yarn wherein one or more false twisting devices are employed.
The patent to Stutz (U.S. Pat. No. 3,543,505) relates to a process for effecting relaxation of the internal tensions of a synthetic textile yarn which has been textured by a first temporary high twisting (a first false-twisting operation) and heat setting in the high twisted state and which has been subjected to a second heat treatment to reduce the elasticity by submitting the yarn to another temporary high-twisting (i.e., a second false twisting) in a direction opposite to that of the first high-twisting and without further heat treatment. As described in the examples of this patent, the second false-twisting step is effected at approximately the same high twist level as the first false twisting step.
Another patent to Stutz (U.S. Pat. No. 3,726,073) discloses a process for compensating internal stresses in a false twisted yarn which is described as overcoming disadvantages of the process of U.S. Pat. No. 3,543,505. In this process both high twisting treatments are effected by a combined false-twisting device having a twist tube and a friction twist imparter driven by a common drive roller. The further twist imparter employs a pair of O-rings at opposite ends of a tubular element for imparting the second high twist treatment to the yarn.
U.S. Pat. No. 3,874,156 discloses a dual yarn texturing operation wherein a yarn is simultaneously subjected to edge crimping and to false twisting to provide an unbalanced high crimp yarn having lower torque than that of conventional yarns of the equal crimp produced by a false twister alone.